The present invention relates generally to semiconductor manufacturing processes, and more particularly to methods and apparatus for controlling resist residue defects at Polysilicon Gate layer in a semiconductor device manufacturing process.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there have been and continue to be efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such high device packing densities, smaller and smaller feature sizes are required. The requirement of small features (and close spacing between adjacent features) requires high resolution lithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the photoresist. The photoresist coated substrate is baked to evaporate any solvent in the photoresist composition and to fix the photoresist coating onto the substrate.
The baked coated surface of the substrate is next subjected to selective radiation using a mask, wherein the mask is employed to effect an image-wise exposure to actinic radiation. The masking step is used to protect one area of the wafer while working on another. Alignment apparatus aligns the wafer to the mask, and then projects an intense light through the mask and through a series of reducing lenses, exposing the photoresist with the mask pattern. The mask permits radiation to contact certain areas of the photoresist and prevents radiation from contacting other areas of the photoresist. This selective radiation exposure causes a chemical transformation in the exposed areas of the photoresist coated surface. Types of radiation commonly used in microlithographic processes include visible light, ultraviolet (UV) light, deep ultraviolet (DUV) light and electron beam radiant energy. After selective exposure, the photoresist coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist (depending upon whether a positive or a negative photoresist is utilized) resulting in a patterned or developed photoresist, exposing the underlying layer (e.g., oxide) previously deposited. The portions of the underlying layer not protected by the hardened resist layer may now be etched away, by, for example, a chemical solution or plasma gas discharge, or may otherwise be operated on.
Due to the large number of critical masking steps in a modern process flow and the inherent ability to impact pattern fidelity, photolithographic defects are particularly dangerous. The ability to detect and eliminate new defect types becomes increasingly important as integrated circuit device geometries continue to shrink into the deep sub-micron regime. Post-develop residue is a common defect phenomenon particularly in DUV lithography which occurs at a critical mask layer. For example, post-develop defects may occur at an active mask layer on a nitride film and/or at a Gate mask on a polysilicon/silicon oxide film or on a silicon nitride BARC (bottom anti-reflective coating) film.
Formation of post-develop or resist residue defects commonly occurs during a pattern image transfer associated with a lithography process. As a result of irradiating a photoresist through a photomask, resist residue or byproducts often form on the photoresist. A developer solution is then deposited over the selectively irradiated photoresist. However, the solubility of the radiation sensitive Photo Acid Generator (PAG) contained in the photoresist can be low. Moreover, it is believed that low solubility rates of the PAG in the developer are exacerbated by the presence of impurities (calcium, sulfur), which cause exposed (open) regions of the resist to be incompletely dissolved in the developer solution within a common process time (typically a 30 to 60 second develop time). As a result, circular defects are generated and remain on the wafer at the completion of the development cycle.
If the resist residue (resist byproducts) contains impurities, such as carbon, calcium (such as in the form of CaF), nitrogen and/or sulfur, the defects become robust enough to withstand decay during a subsequent Barc (bottom anti-reflective coating)/Polysilicon etch process. Hence, poor fidelity of the desired pattern at that layer results (the defects prevent processing of the underlying layer). These post-develop defects tend to have a circular appearance and thus are typically referred to as circular, satellite or cluster defects. Due to their subtle physical characteristics and low density, these defects are often dismissed as non-fatal defects. However, they may contribute to yield loss and raise device reliability issues because of the sheer volume (hundreds to thousands) of such defects on the wafer. In addition, despite their subtle physical characteristics, they can undesirably act as a hard mask, resulting in pattern deformation after etch. Thus, pattern deformation poses a substantial yield risk. In light of these problems, there is an unmet need for detecting, reducing and controlling the presence of post-develop defects at critical mask layers.
The following presents a simplified summary of the invention in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention. It is intended to neither identify key or critical elements of the invention, nor to delineate the scope of the present invention. Rather, the sole purpose of this summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented hereinafter. The present invention provides methods and apparatus for controlling resist residue defects in a semiconductor device manufacturing process.
According to one aspect of the present invention, a method is provided for reducing resist residue defects in a semiconductor manufacturing process, comprising applying a photoresist coat to a semiconductor substrate structure, selectively exposing a first portion of the photoresist coat using an exposure source and a photomask, wherein a second portion of the photoresist is unexposed. The method further comprises developing the first portion of the photoresist using a developer, removing the developed first portion of the photoresist from the structure, and removing resist residues from the structure in order to reduce resist residue defects.
The resist residue defects may be reduced, for example, by applying an anti-reflective coating to the structure prior to applying the photoresist coat, wherein the anti-reflective coating comprises SiON. The invention can also include exhausting resist residue from the structure during development at a rate of between about 5 to 6 meters per second air velocity, and rinsing the structure using a plurality of rinse nozzles selectively applying rinsing fluid to the structure from generally opposite sides thereof. Further defect reductions may be achieved by applying deionized water to the structure, wherein the deionized water is heated to at least about 40 degrees C. The method may alternatively or in combination comprise performing a vapor priming operation of short duration using a mild priming agent prior to applying the photoresist, and/or using a developer with a surfactant. Other techniques may be included in the method for reducing such defects, such as baking the structure at a high post exposure bake (PBE) temperature, and/or extra rinsing the structure with deionized water for at least about 40 seconds extra over standard rinse time (20-30 sec).
Another aspect of the invention provides systems for reducing resist residue defects in a semiconductor manufacturing process, comprising means for applying a photoresist coat to a semiconductor substrate structure, for selectively exposing a first portion of the photoresist coat using an exposure source and a photomask, wherein a second portion of the photoresist is unexposed, for developing the first portion of the photoresist using a developer, for removing the developed first portion of the photoresist from the structure, and means for removing resist residues from the structure in order to reduce resist residue defects.
To the accomplishment of the foregoing and related ends, the invention involves the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other aspects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.